This invention relates to a process for the preparation of compressed baker's yeast or dry baker's yeast with improved activity or leavening power in an acid medium, the compressed baker's yeast or dried baker's yeast prepared by this process and to bread and to pastry products obtained using this baker's yeast.
Compressed baker's yeast and dry baker's yeast prepared by the usual processes generally have a good activity or leavening power in both unsugared and sugared neutral doughs but their leavening power is unsatisfactory in acid doughs in the presence of organic acids such as acetic acid, propionic acid or lactic acid. Below certain pH values, these acids considerably inhibit the fermentation produced by the usual baker's yeasts.
Many types of bread require the presence or use of both the aforesaid acids and baker's yeast for their production. Thus, for example, propionic acid and its salts, which have a fungistatic action in an acid pH, are frequently used in the bread industry to prevent the formation of mold in packaged, sliced bread which can be toasted and as constituents of many baking additives employed in the production of such packaged, sliced breads. In fact, it is only the use of these fungistatic substances which has made it possible for packaged, sliced bread with a long shelf life to be manufactured on an industrial scale.
The packaged, sliced bread designed for toasting has uniform slices with a thin pliable crust in contrast to breads of the European type which are not customarily sold in presliced condition and which usually have a relatively thick, nonpliable crust.
Furthermore, the addition of calcium acetate or acetic acid to the dough is recommended, for example, to prevent a so-called ropiness or stringiness in the manufacture of unacidified bread. In the manufacture of mixed breads containing rye flour, of the types which are particularly common in the Federal Republic of Germany, organic acids are added to the dough or formed during the fermentation process. The organic acids used for this purpose, in this case mostly acetic acid and lactic acid, considerably improve the baking properties of rye flour. Acetic acid and lactic acid are either produced by the bacterial flora during manufacture of these rye mixed breads, for example, when the Berlin short leavening method is used, or they are added directly to the dough in the dry leavening method and the finished leavening method.
The experiments described below are included to demonstrate the reduction in the leavening activity of fresh baker's yeast (compressed yeast) by the addition of acid substances to the dough. Two commercial fresh baker's yeasts A and B, for the bakery trade, were used for the experiments. 1.35 gm of the yeast, based on the content of dry substance in the yeast, were mixed in each case with 280 gm of wheat flour, 3.9 gm of cooking salt and 156 ml of tap water to form a dough. The water was previously warmed up so that the dough was at a temperature of 30.degree. C. after it had been kneaded for 5 minutes. The results of the tests are indicated in Table I below. The quantity of substances added is given in percentages, based on the quantity of flour used. The leavening activity of the yeasts was determined over a period of 2 hours at 30.degree. C. in the Fermentograph manufactured by Brabender, Duisburg, and is given as ml of carbon dioxide.
TABLE 1 ______________________________________ Reduction in Leavening Activity of Fresh Baker's Yeast (Compressed Yeast) by Pres- ence of Acid-Reacting Additives in the Dough Leavening Activity % Activity of Yeast Additive ml CO.sub.2 the Controls ______________________________________ A -- 1010 100 0.5% calcium propionate 600 59 0.5% calcium acetate 930 92.1 1% of 80% lactic acid 790 78.2 B -- 1050 100 0.5% calcium propionate 660 62.8 0.5% calcium acetate 910 90.1 1% of 80% lactic acid 840 80 ______________________________________
The extent to which the additivies in the dough inhibited the leavening activity of the yeast was approximately the same for both of the commercial fresh baker's yeasts and was in the region of 8% to 41% depending on the type of acid-reacting additive. The inhibitory effect of the additives can be further increased by lowering the pH of the dough. In test doughs containing calcium propionate and calcium acetate as additives, the pH was 6.6; in the test dough containing lactic acid the pH was 4.7. In sour dough, the pH may even fall to 4.0.
When the dough recipe is used which is even closer to that used in practice, to which has been added a commercial baking additive for packaged, sliced bread containing approximately 10% of propionate as calcium propionate, the effect of the presence of the short chain carboxylic acid salt in reducing the leavening power of the yeast is even more significant.
The reduction in leavening activity is particularly pronounced in the case of dry baker's yeast. Substitution of fresh baker's yeast by active dry baker's yeast in this field of bakery products has, therefore, hitherto not been possible owing to the lack of leavening power of dry baker's yeast in doughs which have a high degree of acidity or to which carboxylic acids have been added.
The leavening power of commercial fresh baker's yeast is compared below with that of commercial instant dry baker's yeast in a dough used for the manufacture of mold-proof packaged, sliced bread. For the experiment, a dough was prepared from 1000 gm of type 550 wheat flour, 590 gm of water, 21 gm of dry yeast substance (corresponding to 70 gm of fresh baker's yeast or 23 gm of instant dry baker's yeast), 20 gm of salt, 40 gm of fat and 75 gm of a baking additive for packaged, sliced bread dough with a mold-protective agent (calcium propionate). The dough was at a temperature of 30.degree. C. 250 gm batches of the dough were incubated in a Brabender Fermentograph for 50 minutes at 30.degree. C. The results for the leavening activity obtained are entered in Table 2 below.
TABLE 2 ______________________________________ Comparison of the Leavening Activity of Commercial Fresh Baker's Yeast with That of Instant Dry Baker's Yeast in a Dough for Packaged, Sliced Bread Con- taining Mold Protective Agent Leavening Activity ml CO.sub.2 /50 min. ______________________________________ Fresh baker's yeast A 600 Fresh baker's yeast B 630 Instant dry baker's yeast C 360 Instant dry baker's yeast D 380 Comparison: Fresh baker's yeast A without the baking additive with mold protective agent 1400 ______________________________________
The Table shows that good quality fresh baker's yeasts have approximately 40% more leavening power than dry baker's yeast, based on the quantity of dry substance, in a dough for packaged, sliced bread containing commercial baker's additive with a mold protective agent. The substitution of one part of dry baker's yeast (content of dry substance 95%) for 3.16 parts of fresh baker's yeast (content of dry substance 30%), which is theoretically possible, is in this case reduced to a substitution in the proportions of 1:2 in order to obtain the same leavening power.